At ITSF 2023, Jörg Urban addressed new railway network timing and sync requirements, exploring how grandmaster clocks can be combined with atomic cesium solutions to meet the latest global standards.

1. Time and sync requirements
in railway networks
Mario Arnold, synchronization network engineering at DB Netz AG
Jörg Urban, AVP BD at Oscilloquartz, ADTRAN SE
• Deutsche Bahn Netz

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The future of mobility is rail
• Digitalization, automation and artificial
intelligence (AI) are key to a higher capacity and
optimal utilization of the rail network. Our goal is
clear: more attractive rail transport with more
trains, of higher quality. And all without adding a
single meter of new track.
Modernizing
Faster, greener, smoother: thanks to Digitale
Schiene Deutschland
European Train Control System (ETCS)

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Rail sector in transition
• Modernization
• Old SSUs replaced with new sync technology
• SDH to packet network, support for E1 and SyncE
• NTP and PTP …
• New 5G comm technology for rail operation
• Future Railway Mobile Communication System / Europe
• https://uic.org/projects/future-railways-mobile-communications-systems-solutions
• Needed to replace obsoleted GSM-R / ETCS
• Digitalization/Big Data
• Positioning enables efficiency rail track operation
• IoT
• Predictive maintenance
• Smart power grid
• Renewable and decentralized energy supply/production
MODERNIZATION OF THE IT/TELECOM INFRASTRUCTURE INCL. SYNCHRONIZATION

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SLA enabling sync architecture for mission-critical communication networks
The new timing and sync solution
Highly accurate and redundant timekeeping, distribution and assurance
Core network
Ensemble of highly precise and
accurate ePRTCs
< +/-30ns to UTC ePRTC
Aggregation/access network
COs enabled to provide time information
to variety of consumers
Better +/- 100ns (PRTC-A), 40ns (PRTC-B)
4G / 5G
Versatile
edgeSync
Versatile
edgeSync
Enterprises/wholesale
Applications
Better +/- 1000ns to UTC
Sync
network
and
service
management
Smart grid
Time over optical transport
Secure and highly accurate time distribution
MEC / DC
L2/TSN/L3
Fiber/WDM/MW
Access network
ePRTC
ePRTC
Time/phase
Peering

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Modernization of sync network
(High-level sync design)
Objective:
Highly resilient sync architecture at any Deutsche
Bahn ‘Netz’ site,
GNSS jamming and spoofing agnostic

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• SDH, still in use for the next 15 years
• > 5.000 SDH nodes
• Rail track operation (monitoring and control)
• GSM-R, voice and data services
• DWDM & IP/MPLS for each
• ITC services
• Enable 5G rollout replacing GSM-R
• Migration of SDH/PDH-based rail track operation
The network – points of presence (PoPs)
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The SDH sync structure
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‘Clusters’ add redundancy (3 – 4 areas)
52 PRC areas 15 PRC clusters

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• PRC/SSU for E1/SyncE, PTP and NTP application
• PRTC-B capable device
• Performance management capabilities
• T-BC Class C/D support
• High E1 and Ethernet fan-out
• Highly redundant – clock module, PSU & port
• Future-proof with (cn/e)PRTC
• Less power consumption
• High system uptime
• Design approach – simplified architecture and device config.
Versatile edgeSync requirements

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• PTP G8275.1 and SyncE over 1G OTN links
• Max 2 OTN hops, typical measurements, maxTE of 5ns
• For monitoring use the internal measuring function
• A link outage on DWDM/OTN causes phase hits!
• DWDM network to transport phase/time via OTN
edgeSync device monitoring and backup
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• Typical measured maxTE 60ns on monitored PRTC (configuration: GNSS vs PTP input from cnPRTC)
Measurement results
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• PRTC monitoring – 2

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Introducing ePRTC at core sites

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• (cn)ePRTC cluster at each core site
• 2x ePRTCs each connected to 2x Cs clocks
• Interconnection with 10MHz over optical fiber
• 2x dedicated T-BC / Class D devices
• PTP G8275.1 and SyncE input over optical fiber
• Distribution of PTP G8275.1 & SyncE over 1G-OTN
• Interconnect UTC(DT) and UTC(PTB) for research
purposes
• At 2 core sites in each location (Frankfurt and Berlin)
(cn)ePRTC setup

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• edgeGM & T-BC at 5G switch hub (grooming of 5G RRU)
• OTN being used to transport PTP/SyncE, G8275.1
• Plan to build own time scale
• Time sync of 5G radio and application
Next …
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The intended timeline for the introduction of FRMCS by DB
and an overview of the various steps taken, (03 / 2022)

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• We can’t know what we don’t measure
• Synchronization networks require accurate planning
• Internal knowledge transfer about synchronization is necessary
• Keep it simple and stupid (KISS) principle – Perfect is when you can't leave
anything out
Takeaways
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Thank you
For questions please contact:
mario.arnold@deutschebahn.com or joerg.urban@adtran.com